Neumann Vintage U87 Clone : Build Thread.

[pavthefiddler]

Almost finished building my mic. Peluso capsule, tantalum and styrene caps, cinemag trafo. I'm going to replace the cinemag with the tab-funkwerk in the nearest future. I'm using B2 Pro body, with all 3 switches wired to the board. The microphone sounds really good.

I ran into a small difficulty: when I initially assembled everything and did some test recording I noticed a very slight 50 Hz hum (visible on the spectrum analyser, but not really obvious in the recording). Also the high pass filter switch was acting as an antenna (really loud hum when touched or anything near it). I gathered it means that the switch body wasn't grounded properly. Indeed it turns out when I was cutting tracks on the original B2 switch PCB I cut the ground track leading to that switch. When I fixed that the hum is gone but the microphone is barely working - the signal is some 50dB lower than it should be.

I believe it has to be something very simple - a short circuit of some sort most likely. I'm going to try to fix it tomorrow and once it's done I'll post some pictures and sound samples.

 

[wave]

Almost finished building my mic. Peluso capsule, tantalum and styrene caps, cinemag trafo. I'm going to replace the cinemag with the tab-funkwerk in the nearest future. I'm using B2 Pro body, with all 3 switches wired to the board. The microphone sounds really good.

I ran into a small difficulty: when I initially assembled everything and did some test recording I noticed a very slight 50 Hz hum (visible on the spectrum analyser, but not really obvious in the recording). Also the high pass filter switch was acting as an antenna (really loud hum when touched or anything near it). I gathered it means that the switch body wasn't grounded properly. Indeed it turns out when I was cutting tracks on the original B2 switch PCB I cut the ground track leading to that switch. When I fixed that the hum is gone but the microphone is barely working - the signal is some 50dB lower than it should be.

I believe it has to be something very simple - a short circuit of some sort most likely. I'm going to try to fix it tomorrow and once it's done I'll post some pictures and sound samples.

Hi pavthefiddler,
If I may ask, what is the reason that you are going to change the transformer from the Cinemag to the Tab? I'm trying to decide which to get and I'm looking for as many opinions as I can get!
Hope you figure out your level issue.

Thanks,
Dave

 

[saxmonster]

just a quick question?

When i checked the drain to ground volts i had the capsule disconnected as stated but did i need to run a signal through the pads while i was adjusting the pot to get the correct voltage?

thanks
-Scott

 

[kante1603]

Almost finished building my mic. Peluso capsule, tantalum and styrene caps, cinemag trafo. I'm going to replace the cinemag with the tab-funkwerk in the nearest future. I'm using B2 Pro body, with all 3 switches wired to the board. The microphone sounds really good.

I ran into a small difficulty: when I initially assembled everything and did some test recording I noticed a very slight 50 Hz hum (visible on the spectrum analyser, but not really obvious in the recording). Also the high pass filter switch was acting as an antenna (really loud hum when touched or anything near it). I gathered it means that the switch body wasn't grounded properly. Indeed it turns out when I was cutting tracks on the original B2 switch PCB I cut the ground track leading to that switch. When I fixed that the hum is gone but the microphone is barely working - the signal is some 50dB lower than it should be.

I believe it has to be something very simple - a short circuit of some sort most likely. I'm going to try to fix it tomorrow and once it's done I'll post some pictures and sound samples.

Congrats,you seem to be very close to finishing.
I would lift the switch connections on pcb first and try the functionality of them by shorting them dirctly there.This way you can shoot out the switch board.I can't tell you more about it since I can not test it (you all know why..... :.Have only cut this one little trace I mentioned for not shorting the omni position to ground.Having all switches grounded can be essential.Did you twist the wires?-Just an idea....
I bet you have allready cecked continuity through the complete mic body and to the pcb.
This gain issue,does that mean you are 50 dB off or have to make up gain arround 50dB on your pre amp?
Maybe something weird with the trafo connections or swappped?(wasn't there at least one guy here having trouble with lowish level on output by using the cinemag)?
Must go to work now....please keep us informed,all will be good soon I bet,

Udo.

 

[kante1603]

10.7.2 Udo.

Hi,

did a quick test on an OSX 10.7.x some minutes ago:Yes,it works!
Simple tool but very usefull,did not check in-depth but really loved the zoom functions,should be easy to dial the pot in for biasing.I used just what was connected to the computer,a digi 003 in this case,and fed a -50dB-ish sine from a neutrik minirator to mic in ch.1 to simulate a (dynamic) microphone-when using it check preferences for audio on your mac,after that everything is fine.

Thanks for sharing!

Udo

 

[wthrelfall]

Dany, new board and new bom seem to have done the trick - it's working    Happy!
One last thing, how do I set the pattern to figure eight?  put the jumper between "Hyper" and "8"? 

 

[kante1603]

Dany, new board and new bom seem to have done the trick - it's working    Happy!
One last thing, how do I set the pattern to figure eight?  put the jumper between "Hyper" and "8"?

Yes.

Udo.

 

[wthrelfall]

Dany, new board and new bom seem to have done the trick - it's working    Happy!
One last thing, how do I set the pattern to figure eight?  put the jumper between "Hyper" and "8"?

Yes.

Udo.

thought so, but it doesn't work 

 

[kante1603]

Does it work in omni mode?
If not then the voltage for the back capsule seems missing.
Check for shorts as well as back capsule wiring then.

Udo.

 

[wthrelfall]

Does it work in omni mode?

Yes, Omni and cardioid work ok.

 

[kante1603]

Does it work in omni mode?

Yes, Omni and cardioid work ok.

Don't have the schemo handy,I'm at work now.
If the omni mode does really work it can't be too much,maybe just the figure eight connection has a cold solder blob.Trace this point back to the next parts for conntinuity.Compare to the schematics.
For testing omni vs cardioid:If talking to the front you will hear the signal a bit louder than in omni,it will have a level drop in omni mode.Also if talking to the side of the capsule the cardioid mode will get way quieter when moving arround the mic while in omni the sound should not or just very slightly change from front to side.Meaning the cardioid has it's maximum signal rejection at an 90 degree angle.

Udo.

 

[pavthefiddler]

Almost finished building my mic. Peluso capsule, tantalum and styrene caps, cinemag trafo. I'm going to replace the cinemag with the tab-funkwerk in the nearest future. I'm using B2 Pro body, with all 3 switches wired to the board. The microphone sounds really good.

I ran into a small difficulty: when I initially assembled everything and did some test recording I noticed a very slight 50 Hz hum (visible on the spectrum analyser, but not really obvious in the recording). Also the high pass filter switch was acting as an antenna (really loud hum when touched or anything near it). I gathered it means that the switch body wasn't grounded properly. Indeed it turns out when I was cutting tracks on the original B2 switch PCB I cut the ground track leading to that switch. When I fixed that the hum is gone but the microphone is barely working - the signal is some 50dB lower than it should be.

I believe it has to be something very simple - a short circuit of some sort most likely. I'm going to try to fix it tomorrow and once it's done I'll post some pictures and sound samples.

Hi pavthefiddler,
If I may ask, what is the reason that you are going to change the transformer from the Cinemag to the Tab? I'm trying to decide which to get and I'm looking for as many opinions as I can get!
Hope you figure out your level issue.

Thanks,
Dave

I've heard a mic with a Tab transformer before and I really liked the sound, hard to describe the difference but I really liked it. I did a classical recording a few years ago, a vocal + piano in a concert hall (2 mics in a M/S configuration) and the microphones with Tab transformers sounded more 'old style', like an old Deutsche Gramofon recording, that sort of sound. Obviously this is just my impression. But the guy who made the microphones was saying similar things, he really liked using them for classical music. Cinemag is cheaper so I just got one to check it out and I can always order Tab and use cinemag for the next project

I'm just about to tackle the hum problem and hopefully I'll be able to post some sound samples later.

 

[pavthefiddler]

just a quick question?

When i checked the drain to ground volts i had the capsule disconnected as stated but did i need to run a signal through the pads while i was adjusting the pot to get the correct voltage?

thanks
-Scott

I believe the FET drain voltage is constant regardless of whether you inject the signal or not.

 

[kante1603]

I'm just about to tackle the hum problem and hopefully I'll be able to post some sound samples later.

Hi,

So you've got your gain issue solved?

Best,

Udo.

 

[pavthefiddler]

I'm just about to tackle the hum problem and hopefully I'll be able to post some sound samples later.

Hi,

So you've got your gain issue solved?

Best,

Udo.

Yes and no. I disconnected all the wires going to the switches and the output signal level increased. But the whole switch board was still connected to the microphone body (3 screws) and anything near the switches would generate loud hum. I know it means there was a grounding problem. I decided to take the whole switch board out. That solved all the problems -  there is no 50 Hz hum, also the signal to noise ratio increased drastically. I cleaned the switch board with isopropyl alcohol, made sure all switches (their body) are grounded and that there is no short circuits (I cut all the other traces). I put it back in and the problems came back - hum and the RF noise.

So at this stage I decided to get rid of the switch board and switches, at least for the moment. I put the jumpers in and they work great. Would be great to have them, but they are not essential for me. I'm planning a transformer upgrade in a couple of months, I'll attempt to wire the switches again then.

I must say the microphone is quite quiet, it needs a good bit of gain. But the S/N ratio is great so it's not a big deal. It sounds really good. Tonight I'll record some violin samples and photos. Tomorrow I have a great singer coming over so I'll post some vocals too. Friend of mine has the U87Ai so I'm going to compare it to the clone - but I won't get a chance to do that for another couple of days.

Also I might consider removing a layer of the basket mesh, but I need to do some test with the singers first.

Anyway, thank you all, especially Dan and Udo! I learnt a lot and I'm already planning more DIY projects! But time to make some music first...

 

[kante1603]

Yes and no. I disconnected all the wires going to the switches and the output signal level increased. But the whole switch board was still connected to the microphone body (3 screws) and anything near the switches would generate loud hum. I know it means there was a grounding problem. I decided to take the whole switch board out. That solved all the problems -  there is no 50 Hz hum, also the signal to noise ratio increased drastically. I cleaned the switch board with isopropyl alcohol, made sure all switches (their body) are grounded and that there is no short circuits (I cut all the other traces). I put it back in and the problems came back - hum and the RF noise.

Still don´t get it,have measured my switchboard today to make sure everythink is correct.As said I just have cut 1 small trace.
Readings where correct,none of the switches have contact to anything else including ground.The grounds connect properly to the switch shields amongst each other,and considering that the pcb will be mounted back to the 3 metall bolts having full contact to all the metall parts I can not imagine why this happens.
Except of one thing:Given that the switch-construction as acting as an antenna what will it pick up?Something from inside the microphone?I guess no....
So if this is comming from outside (where we have all those nice RF etc.) why isn´t it shielded enough,maybe the tubular part itself isn´t grounded?
All other parts are because they are screwed together so will have continuity from bottom to headbasket,but that does not include the tube.....hmmmmmm....must be put in somewhere....
Did any of the switch wires touch this high sensitive connection between the fet gate and the other board?....Just an idea.....
Holy sh.... -that I can not check it at the moment!
If the same happens to me I would maybe use foil shielded wires with the shield connected to the ground part and the other side left open,but as close as possible to the dedicated board pins to get rid if this.

So at this stage I decided to get rid of the switch board and switches, at least for the moment. I put the jumpers in and they work great. Would be great to have them, but they are not essential for me. I'm planning a transformer upgrade in a couple of months, I'll attempt to wire the switches again then.

I´m very curious now....

I must say the microphone is quite quiet, it needs a good bit of gain. But the S/N ratio is great so it's not a big deal. It sounds really good. Tonight I'll record some violin samples and photos. Tomorrow I have a great singer coming over so I'll post some vocals too. Friend of mine has the U87Ai so I'm going to compare it to the clone - but I won't get a chance to do that for another couple of days.

As said some posts ago I´ll do the same,I have a couple of Ai´s at work which I know very good,exactly from 1986 when they where introduced.
Be aware that they have a different capsule (K67) and have more output;after the math it is a difference of 11dB (-40dBU vs -29dBU) due to changes in the voltage supply part (different filtering and a dc/dc converter added).

Also I might consider removing a layer of the basket mesh, but I need to do some test with the singers first.

?Why?

Anyway, thank you all, especially Dan and Udo! I learnt a lot and I'm already planning more DIY projects! But time to make some music first...

You´re welcome,but I have a bad feeling now....

BTW:What did you use for the 10pF,mica or styrene?

And::Could you post a close up pic of the switch board or have you "closed the file" ;D?

Have fun recording,hope to hear some results soon ,

Udo.

 

[saxmonster]

Does this make sense?

I wanna try to bias it with a scope program on my mac.

So i take a signal generator out of my Daw say on channel one.  Using a 1.4 jack out of channel I cut the end of the wire and solder or clip it to the front capsule pads.  Now the signal will go into the mic.

How do I then get my scope program to see the signal?  Can I hook up a mic chord and plug it into channel two and set the scope program to analyze channel 2?  Then make adjustments to the resistor and output level of the signal?

Obviously I don't have a real scope or probe to use.

Let me know if this will work

-Scott

 

[kante1603]

Does this make sense?

I wanna try to bias it with a scope program on my mac.

So i take a signal generator out of my Daw say on channel one.  Using a 1.4 jack out of channel I cut the end of the wire and solder or clip it to the front capsule pads.  Now the signal will go into the mic.

No, use the measuring input points to inject the signal,the capsule disconnected of course.
Red("RT")=input,black("SW")=ground/0v.

How do I then get my scope program to see the signal?  Can I hook up a mic chord and plug it into channel two and set the scope program to analyze channel 2?

Don´t know neither the program you will use nor the computer you have.Normally the program will have a settings or preferences window where you can set these things.
Yes,you hook up the mics output to a microphone input,using a different channel is always a good idea since you avoid looping back the signal by accident.
After that you must apply phantom power to it,the mic needs it to work. 

Then make adjustments to the resistor and output level of the signal?

Obviously I don't have a real scope or probe to use.

Let me know if this will work

-Scott

Scott,if you are not so familiar in using a scope try to get this working first.Don´t hook the stuff up by now,do an initial trial first as follows:

*Set up your generator to sine wave,1kHz,at a low level of say -50dBU.This will emulate kind of a real expected level from a  microphone.Check if this signal is really comming from say channel 1 by temporarily plugging it to a real micpre (phantom not needed,therefore off).If all is good go to next step.

*Now plug it in to a mic input,say channel 2.You have a prooven kinda mic signal here now.

*Now learn how your scope program acts and behaves.Set it to get the input mic 2 for your measuring.If it has automatic functions for setting the x,y and trigger modes use them!You should see the sinewave now.Go ahead and try to change the x and y settings:The height as well as the width of the sinewave will change corresponding to them.If the wave doesn´t seem to be stable on the screen try toggling through the trigger settings until it works out good.

*If you have passed this little tutorial you can go on and try this with your microphone as described before.If not stop here,you will not risc to damage it,will you

The biasing procedure is well described here in the thread-thanks to matador!!!

Post how it works and have fun,

Udo.

Disclaimer:I am not responsible for you doing something wrong,you must understand using things like a scope basically at least.

 

[saxmonster]

Ok kante, I actually understand everything u said.  Whooooooo!!!!!  Can I actually damage the mic?  What can happen. To damage it.  Will to hot of a signal do the damage.  Just don't want to fry anything but I do want to optimize this mic to its fullest.  Thanks for the info guys.

 

[kante1603]

Ok kante, I actually understand everything u said.  Whooooooo!!!!!  Can I actually damage the mic?  What can happen. To damage it.  Will to hot of a signal do the damage.  Just don't want to fry anything but I do want to optimize this mic to its fullest.  Thanks for the info guys.

Hahaha.....,no,you won't damage it immediately,this was more meant to be very carefull and always being aware what you're doing(forgive me,I'm german and must still learn a lot,especially putting in the right words in english).
Concerning a too hot signal-no,you will use a 0dB sine at 1 kHz at a starting point to be injected at the measuring input.With the scope connected you will see a wave come up at a certain point.I measured the drain voltage in parallel on my dmm to get a rough idea where I'm at and not having to screw the full 25 windings on the pot.Moving the pot screw back and forth will change the symmetry of it.Try to get it in a good balance.
This is best seen at a lower generator signal first for just showing a sine wave.When boosting the generator the wave will start to flatten out,either at the top or bottom.The goal is to get both to flatten out the same way,this is the symmetric clipping.By increasing and decreasing the generator output you can play with it,zooming in on the scope will help to find this point more and more accurate.
It takes a while but is a fun thing to do.
Btw,if you monitor this procedure with your headphones you can clearly hear this spot since a sine wave doesn't have overtones (pay attention to the listening levels).I find this way pretty nice because you audition something while getting a visiual feedback.Not bad.

Happy biasing,

Udo.